An imaging optic of this kind is disclosed, for example, in U.S. Pat. No. 6,903,875. The imaging optic for the display unit is computed for an emmetropic eye. A disadvantage is that a user whose eye is ametropic must make an ametropic correction.
The solution described in U.S. Pat. No. 6,977,776 uses an HMD device which is attached to a spectacles frame.
In United States patent publication 2006/0164730, the suggestion is made to attach the HMD device to the spectacle lens.
U.S. Pat. No. 6,945,648 describes an HMD device which includes a receptacle with which lenses of different corrective strength can be exchangeably held.
The wearing of the HMD device together with the spectacles is, however, often viewed as being unpleasant. The HMD device must either be adapted individually or special spectacle lenses must be held in supply which can be exchanged.
In each case, an ametropic correction is associated with considerable complexity insofar as this correction is even provided for.
U.S. Pat. No. 6,747,611 discloses an HMD device wherein an adjustment of the focus takes place with the aid of a knurled screw which is mounted laterally on the HMD device at the elevation of the spectacles frame. Illumination, microdisplay and a lens are displaced along their optical axes. It is a disadvantage that the knurled screws project at both sides of the head of the wearer.
An HMD device is described in U.S. Pat. No. 5,880,773 wherein an adjustment of the focus takes place via a knurled screw which is mounted on both sides of the nose above the eyes. The transmission of the movement of the knurled screw to a lens, which is to be displaced, takes place via a toothed wheel gear assembly which drives a cam gear which, in turn, moves the lens along the optical axis. The arrangement is technically complex.
A coarse adjustment and a fine adjustment for the focus adjustment are suggested in Japanese patent publication 07234375 A. The coarse and fine adjustments include displacement elements which project outwardly out from the HMD device above each eye. The arrangement is difficult to operate and is technically complex and has a comparatively large length expansion.